A fast grid generation algorithm for local irregular parts of hexagonal discrete global grid systems

Discrete Global Grid Systems (DGGS) provide a multi-resolution discrete representation of the Earth and are preferable for the organization, integration, and analysis of large and multi-source geospatial datasets. Generating grids for the area of interest is usually the premise and basis for DGGS applications. Owing to incongruent hierarchies that restrict the multi-resolution applications of hexagonal DGGS, current grid generation of hexagonal DGGS for local areas mainly depends on inefficient single-resolution traversal methods by judging the spatial relationship between each cell and the area. This study designs a fast generation algorithm for local parts of hexagonal DGGS based on the hierarchical properties of DGGS. A partition structure at intervals of multiple levels is first designed to ensure the coverage relevance between parent and children cells of different levels. Based on this structure, the algorithm begins with coarser resolution grids and recursively decomposes them into the target resolution, with multiple decomposition patterns used and a unique condition proposed to make the generated grids without gaps or overlaps. Efficient integer coordinate operations are used to generate the vast majority of cells. Experimental results show that the proposed algorithm achieves a significant improvement in efficiency. In the aperture 4 hexagonal DGGS, the efficiency ratio of the proposed and traversal algorithms increases from six times in level 14 to approximately 339 times in level 18. This study provides a solid foundation for subsequent data quantization and multi-resolution applications in hexagonal DGGS and has broad prospects.</p

Polyaniline-Assisted Synthesis of Si@C/RGO as Anode Material for Rechargeable Lithium-Ion Batteries

A novel approach to fabricate Si@carbon/reduced graphene oxides composite (Si@C/RGO) assisted by polyaniline (PANI) is developed. Here, PANI not only serves as “glue” to combine Si nanoparticles with graphene oxides through electrostatic attraction but also can be pyrolyzed as carbon layer coated on Si particles during subsequent annealing treatment. The assembled composite delivers high reversible capacity of 1121 mAh g^–1 at a current density of 0.9 A g^–1 over 230 cycles with improved initial Coulombic efficiency of 81.1%, while the bare Si and Si@carbon only retain specific capacity of 50 and 495 mAh g^–1 at 0.3 A g^–1 after 50 cycles, respectively. The enhanced electrochemical performance of Si@C/RGO can be attributed to the dual protection of carbon layer and graphene sheets, which are synergistically capable of overcoming the drawbacks of inner Si particles such as huge volume change and low conductivity and providing protective and conductive matrix to buffer the volume variation, prevent the Si particles from aggregating, enhance the conductivity, and stabilize the solid–electrolyte interface membrane during cycling. Importantly, this method opens a novel, universal graphene coating strategy, which can be extended to other fascinating anode and cathode materials

B,N-Co-doped Graphene Supported Sulfur for Superior Stable Li–S Half Cell and Ge–S Full Battery

B,N-Co-doped graphene supported sulfur (S@BNG) composite is synthesized by using melamine diborate as precursor. XPS spectra illustrates that BNG with a high percentage and dispersive B, N (B = 13.47%, N = 9.17%) and abundant pyridinic-N and N–B/NB bond, show strong interaction with Li₂S_<i>x</i> proved by adsorption simulation experiments. As cathode for Li–S half cell, S@BNG with a sulfur content of 75% displays a reversible capacity of 765 mA h g^–1 at 1 C even after 500 cycles (a low fading rate of 0.027% per cycle). Even at a high sulfur loading of 4.73 mg cm^–2, S@BNG still shows a high and stable areal capacity of 3.5 mA h cm^–2 after 48 cycles. When S@BNG composite as cathode combines with high performance lithiated Ge anode (discharge capacity of 1138 mA h g^–1 over 1000 cycles at 1 C in half cell), the assembled Ge–S full battery exhibits a superior capacity of 530 mA h g^–1 over 500 cycles at the rate of 1 C

Structural Transformation in a Sulfurized Polymer Cathode to Enable Long-Life Rechargeable Lithium–Sulfur Batteries

Sulfurized polyacrylonitrile (SPAN) represents a class of sulfur-bonded polymers, which have shown thousands of stable cycles as a cathode in lithium–sulfur batteries. However, the exact molecular structure and its electrochemical reaction mechanism remain unclear. Most significantly, SPAN shows an over 25% 1st cycle irreversible capacity loss before exhibiting perfect reversibility for subsequent cycles. Here, with a SPAN thin-film platform and an array of analytical tools, we show that the SPAN capacity loss is associated with intramolecular dehydrogenation along with the loss of sulfur. This results in an increase in the aromaticity of the structure, which is corroborated by a >100× increase in electronic conductivity. We also discovered that the conductive carbon additive in the cathode is instrumental in driving the reaction to completion. Based on the proposed mechanism, we have developed a synthesis procedure to eliminate more than 50% of the irreversible capacity loss. Our insights into the reaction mechanism provide a blueprint for the design of high-performance sulfurized polymer cathode materials